Biodegradation of Petroleum Hydrocarbons in the Deep Sea

The Deepwater Horizon (DWH) discharge is unique in that it represents the first large spill that occurred in the deep sea, and unparalleled volumes of chemical dispersant were applied during emergency response efforts. Thus, the DWH incident raised new challenges with regard to predictions of petroleum hydrocarbon (PHC) biodegradation and the fate of discharged hydrocarbons in the deep sea, which is permanently cold (~4 °C) and exposed to high hydrostatic pressure (1 MPa per 100 m). Although extensive information is available on the rates and controls of PHC biodegradation in marine environments, relatively few studies have been conducted under conditions resembling the deep sea. In particular, hydrostatic pressure is a key environmental parameter that has been largely overlooked in biodegradation studies, due to methodological challenges and the difficulty to obtain samples. Considering the rapid expansion of oil and gas drilling into deeper waters, there is an urgent need to improve understanding of the influence of low temperature and high pressure on biodegradation in order to better constrain the fate of hydrocarbons in the deep sea. This chapter addresses the current understanding of deep sea PHC biodegradation, highlighting discoveries made during the scientific response to the DWH disaster.